1. Field of the Invention
This invention lies generally in the field of meat adherent, cook-in containers, particularly containers utilizing multilayered formable packaging web structures.
2. Prior Art
The prior art teaches that a fill-conforming, heat-shrinkable meat-adherent plastic container comprised of hot blown olefinic polymer film, such as polyethylene, or ionomers of ethylene acid copolymers, can be used for cook-in of a meat or other highly proteinaceous product packaged therein with limited cook-out of fluids from the meat into the bag interior (see for examples, Thompson U.S. Pat. No. 4,411,919 and Baird, Jr. et al U.S. Pat. No. 3,294,621 and Packaging Digest of May 1982, pages 50-56). Packages for food have included ethylene acid copolymer film surfaces heat sealed to each other at portions of the package periphery. Such packages are shown in Raines U.S. Pat. No. 4,656,068. There, however, the package had at least one side constructed as a peelable seal with the ethylene acid copolymer contacting an unlike outer surface of polyethylene/ethylene vinyl acetate. Further, the package was not described as a cook-in package and in no way suggested any meat product cook-in capabilities for the ethylene acid copolymer or ethylene acid copolymer ionomer layer employed with polyethylene/ethylene vinyl acetate to provide the readily peelable package side seal. See also Stillman U.S. Pat. No. 4,101,711 showing a non-cook meat by having an ethylene acid copolymer layer adjacent the meat.
Cook-in prior art such as Thompson U.S. Pat. No. 4,411,919 or Packaging Digest, mentioned above, provide no basis for belief that a non-irradiated ethylene acid copolymer film in contact with meat product and sealed to itself would provide a superior cook-in performance with minimal purge and satisfactory seal, as has been found by applicants. Since in the packaged meat trade an appreciable (perhaps up to about 40 weight percent of the total fill) of water is conventionally compounded with the meat to be cooked in such a plastic container, the provision of plastic container structures which permit meat cook-in with substantially no purge presents a formidable technological problem. In effect, in a purge-free system of plastic container and meat (high protein) fill, the added water is taken up and retained by the meat tissue and does not exude or collect during or after cooking as a fluid (or juice) pocket located between the container wall and the fill. Unfortunately, such a pocket or fluid layer when present is typically readily visible to the consumer through such container wall which is typically a virtually transparent packaging material.
Purge avoidance in this field is achieved through the provision of plastic containers whose inner wall is characterized by an ability to adhere to the meat particularly during the cooking temperatures, which typically range from about 150.degree. to 190.degree. F. (More preferably from about 155.degree. to 180.degree. F.) As those familiar with fill formulations appreciate, it is sometimes possible to regulate adherency characteristics between a meat fill and a meat adhering container by compositional variations in the fill formulations. A close, face-to-face adjacent relationship between the container and the meat fill is achieved either by using a shape conforming container structure (such as a resilient casing) which can be literally stuffed with the meat , or by using a container structure which heat shrinks around the meat fill preferably at cooking temperatures.
Two classes of container structures can be identified in the prior art which can achieve the objective of being purge-free. One class comprises flexible non-formable so-called shrink bags and casing structures into which the meat fill is directly packed. The other class of container structures involves the use of a starting formable web member which is preformed into a desired tray configuration, size, or the like before being filled with meat and sealed with a (usually non-formable) lid web member. In the first class of such container structures, it is typical to employ relatively thin (usually less than about 4 mils) walled materials. In the second class, the formable web, or tray, member typically ranges from about 8 to 14 mils in thickness while the lid web member typically ranges from about 4 to 8 mils in thickness.
The web structures employed in such second class of container structures are typically in the form of multi-layered webs or laminates wherein each layer individually serves one or more functions and wherein all layers coact together to provide a container wall structure which protects the fill from the environment in a package system and which also provides thermal stability, meat adherency and heat-shrink characteristics suitable for the firm, fill and cook operations. The interaction between the layer, is important, and, unless a suitable balance of properties exists in a given web, successful production of a cooked-in package meat product having no purge is not obtainable. Usually in the assembled package of formed container and meat fills the tray portion thereof is substantially more heat shrinkable than the lid portion; this is achieved by using selected low temperature tray forming conditions upon the starting formable web so that during forming the formable web, is, in effect, stretched and "frozen" in such configuration. Thereafter, following filling and sealing, the tray at cooking temperatures tends to shrink or "snap back" towards its starting dimensions thereby closely enveloping the meat fill as desired to avoid purge. The inner container surface portions must be suitable for food contact usage and must also be meat adherent. The formable web structure must be such as to permit tray formation, particularly under draw conditions without degradation. A good heat seal is required between contacting portions of, respectively, the tray rim portions and the lid member edge portions in order to avoid leakage, contamination, or the like even under cooking conditions. The entire container structure must be adapted for post-cooking storage of a meat fill therein at temperatures less than ambient. Package shape retention after packing and sealing and particularly during the cooking step is a particularly desirable feature associated with such second class of container structure. Because of such criteria and performance requirements, it is generally recognized in the field that it is more difficult to manufacture purge-free containers of such second class than of such first class.
There continues to exist a need for new and improved formable purge-free container structures having characteristic generally as above described, which can be produced at sufficiently low cost to make possible their production and use on a commercial scale in the cook-in meat packaging trade.